The Prophet ﷺ said: Set the rows in order, stand shoulder to shoulder, close the gaps, be pliant in the hands of your brethren, and do not leave openings for the devil. If anyone joins up a row, Allah will join him up, but if anyone breaks a row, Allah will cut him off. Abu Dawud said: The name of Abu Shjrah is Kathir b. Murrah. (Using translation from Abū Dāʾūd 666)
"أقيموا الصُّفوفَ؛ فإِنَّما تَصُفونَ بِصُفُوف المَلَائكَةَ، وحاذُوا بين المنَاكِبِ، وسُدُّوا والخَلَل، وليِنُوا بأيدى إخوانكم، ولا تَذَرُوا فُرُجاتٍ للشَّيطان، ومن وَصَلَ صَفًا وصله اللهُ، ومن قطع صَفًا قطعه اللهُ".